Since the 1970's, government legislation has required increasing reductions of NOx in exhaust gas emissions. To comply with increasingly stringent government mandates, industry has developed several EGR (Exhaust Gas Recirculation) systems, which re-circulate the exhaust gas to reduce the NOx gas emissions. At the same time, government regulations are requiring on-board diagnostics (OBD) on heavy duty gasoline and diesel engines to monitor the functioning of emission control components and alert the vehicle operator to any detected need for emission-related repair.
Emissions targets for 2010 and beyond require the use of extreme high fidelity EGR flow measurement to control NOx during engine transients, as well as to provide precise measurement of EGR flow resulting from exhaust manifold pulsations. In modern Diesel engines, the air-handling system is tightly controlled so as to obtain the commanded amount of EGR which is determined by the combustion recipe. The presence of a fault in the EGR handling system (e.g., a restriction, a leak or a faulty sensor/actuator) would lead to the wrong amount of EGR being delivered at the wrong amount of time. This leads to an emission exceedance of either NOx or particulate matter (PM).
In addition to an EGR system, emissions requirements are requiring increasing performance from other internal combustion engine subsystems. For example, three major closed-loop control systems in modern diesel engines involve controls for the air-handling system that control and regulate the amount of fresh air-flow and EGR flow that is sent into the engine's cylinder, controls for the fuel system that controls the timing and the amount of fuel that is injected into the cylinder, and controls the exhaust aftertreatment system, such as a SCR system.